In certain signal lamp installations, such as, in railroad-highway crossing warning apparatus, flashing lights are used to visually forewarn oncoming motorists and pedes trians of approaching trains and/or mass transit vehicles. In typical highway crossing signal lamp units, an incandescent light bulb having a concentrated filament is used in combination with an adjustable socket bracket, a parabolic reflective mirror and a colored lens to project the parallel light rays in a predetermined direction. In order to maximize the effectiveness of the parabolic reflector, it is essential that the light-emitting filament of the incandescent light bulb must be located at the focal point of the parabola. Under such a condition, the impinging radiant energy or light rays are reflected in a parallel direction from the surface of the parabolic mirror so that a highly concentrated source of light is viewed by even distant motorists in plenty of time to stop their vehicles as they approach the highway crossing. Thus, it will be seen that this precise focusing of the light bulb allows the motorists to be alerted at substantially a greater distance from the crossing than if the filament was not situated of the focal point of the parabolic reflective mirror. In prior art signal lamp units, it was common practice to employ integral sighting tubes or finders to determine when the filament of the lamp was situated at the focal point of the concave mirror. It will be appreciated that such an integral sighting device, which included a sight tube carrying a lens and a ground glass plate having cross-hairs upon which an image of the filament was focused, not only increases the initial purchase cost but also results in a somewhat heavier and bulkier signal lamp unit. In addition, there were other prior art focusing devices which took the form of jigs which could be repeatedly used on and transferred from one lamp unit to the next in establishing the focal point of a lens of reflective mirror. However, these previous lamp filament locators were relatively complex and were normally designed for a specific type or model of signal lamp units. Thus, while these prior art types of focal point finders were usually successfully used in locating and positioning the filament of a light bulb at the focal point of a lens or reflector in signal lamp units, they were relatively expensive to make and were highly complex to set up and operate. In addition to their initial manufacturing cost, these removable sighting devices were expensive to operate since they required an undue amount of time to attach and detach them to the lamp units. Thus, it is desirable and highly advantageous to utilize an inexpensive and simple sighting device which may be quickly and easily mounted to the signal lamp units for effectively focusing in the filament of a light bulb and which may be facilely and readily disconnected therefrom. Further, the proposed focal point sighting device should be adapted for universal usage on various models or types of signal lamp units. Hence, in order to maximize the efficiency of a signal lamp unit at the least cost, it is fundamental to provide a unique method of quickly and easily sighting in and locating the filament of a light bulb at the focal point of a parabolic mirror.